Read values from root file

ROOT
5

For completeness and future reference, your snippet would look like the following with TTreeReader (modulo typos :slight_smile: ):

// the two repeated snippets should be made into a single function called twice
void read() {
  TFile fsig("susysignal_total.root");
  TTreeReader rsignal("signal_Tree", &fsig);
  TTreeReaderValue<double> energytop_sig(rsignal, "energytop1");
  auto histo_sig = new TH1D("histo", "", 100, 0., 2200.);
  while(rsignal.Next())
    histo_sig->Fill(*energytop_sig);

  TFile fbg("susybackground_total.root");
  TTreeReader rbg("susybg_Tree", &fbg);
  TTreeReaderValue<double> energytop_bg(rbg, "energytop1");
  auto histo_bg = new TH1D("histo", "", 100, 0., 2200.);
  while(rbg.Next())
    histo_bg->Fill(*energytop_bg);

  histo_sig->Draw();
  histo_bg->Draw("same");
}

and like the following with TDataFrame:

// the two repeated snippets should be made into a single function called twice
using namespace ROOT::Experimental;
void read() {
   TDataFrame dfsig("signal_Tree", "susysignal_total.root");
   auto histo_sig = dfsig.Histo1D("energytop1");
   histo_sig->Draw();

   TDataFrame dfbg("susybg_Tree", "susybackground_total.root");
   auto histo_bg = dfbg.Histo1D("energytop1");
   histo_bg->Draw("same");
}